Optimized system selection using location estimation

ABSTRACT

A current location of a mobile system in a wireless network can be determined by using information provided by a base station in communication with the mobile system. The information can include a system identifier (SID) table and a local time offset (LTM_OFF) value and a daylight savings time (DAYLT) value. The SID table is used to provide a mobile country code (MCC) associated with a country in which the mobile device is located. The LTM_OFF value is used to provide a range of longitude values in which the mobile device is located. The current location of the mobile device is based upon at least the range of longitude values and the current country. The current location is used to build an optimized scan list that is used, in turn, to identify and acquire access to the preferred system by a mobile device.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application takes priority under 35 U.S.C. 119(e) of thefollowing U.S. Provisional Patent Applications entitled:

-   -   (i) GEO TAGGING USING LOCATION ESTIMATION by Rao et. al. having        Ser. No. 61/417,067 filed Nov. 24, 2010 that is incorporated by        reference in its entirety for all purposes;    -   (ii) OPTIMIZED SYSTEM SELECTION USING LOCATION ESTIMATION by Rao        et. al. having Ser. No. 61/417,072 filed Nov. 24, 2010 that is        incorporated by reference in its entirety for all purposes; and    -   (iii) LOCATION ESTIMATION by Rao et. al. having Ser. No.        61/417,074 filed Nov. 24, 2010 that is incorporated by reference        in its entirety for all purposes.

This patent application is related to the following co-pending U.S.patent applications each of which are incorporated by reference in theirentireties for all reasons:

-   -   (i) U.S. patent application Ser. No. 13/110,835 entitled        “LOCATION ESTIMATION”, by Rao et. al. filed May 18, 2011; and    -   (ii) U.S. patent application Ser. No. 13/110,840 entitled “GEO        TAGGING USING LOCATION ESTIMATION”, by Rao et. al. filed May 18,        2011.

TECHNICAL FIELD

The embodiments described herein relate generally to the field ofwireless communication. In particular, using location estimation toprovide improved carrier selection by a mobile system in a wirelessnetwork is described.

BACKGROUND

Wireless communication networks are widely deployed to provide variouscommunication services, such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting communication for multiple users by sharing theavailable network resources. Examples of such multiple-access networksinclude Code Division Multiple Access (CDMA) networks, Time DivisionMultiple Access (TDMA) networks, Frequency Division Multiple Access(FDMA) networks, and Orthogonal FDMA (OFDMA) networks.

It is often desirable, and sometimes necessary, to know the location ofa terminal in a wireless network. The terms “location” and “position”are synonymous and are used interchangeably herein. For example, a usermay utilize the terminal to browse websites and may click on locationsensitive content. The location of the terminal may then be determinedand used to provide appropriate content to the user. There are manyother scenarios in which knowledge of the location of the terminal isuseful or necessary.

Various positioning methods may be used to determine the location of aterminal. Each positioning method may use certain information and mayrequire certain capabilities at the terminal and/or a location server inorder to compute a location estimate for the terminal. It is desirableto support positioning in an efficient manner in order to conserveresources and reduce delay.

Using efficient location estimation to reduce an amount of time requiredto identify an appropriate carrier for a mobile system (MS) that canalso reduce an amount of power consumed.

SUMMARY OF THE DESCRIBED EMBODIMENTS

Other apparatuses, methods, features and advantages of the describedembodiments will be or will become apparent to one with skill in the artupon examination of the following figures and detailed description. Itis intended that all such additional apparatuses, methods, features andadvantages be included within this description be within the scope ofand protected by the accompanying claims.

A method performed in a wireless communication network can be carriedout by receiving information corresponding to a location of a mobilesystem, using the location information to identify a preferred system,and acquiring service associated with the preferred system.

In one aspect, the preferred system is identified by accessing a taggedGEO Locate Table that includes at least one GEO tagged withcorresponding location information, indexing the tagged GEO Locate Tablewith the location information corresponding to the acquired service, andidentifying the preferred system in accordance with the indexing. TheGEO Locate Table includes at least a system identifier (SID), acorresponding GEO identifier, a device location, a channel number, and aPreferred Roaming List (PRL) indicator indicating that the SID isprovisioned in a PRL stored in the mobile system.

A wireless mobile system includes at least a wireless interface, thewireless interface configured for wirelessly communication with awireless base station, a memory device arranged to store data, the dataincluding at least a preferred roaming list (PRL), and a processorcoupled to the wireless interface and the memory device, the processorarranged to acquire access to a preferred system by, receivinginformation corresponding to a location of a mobile system, using thelocation information to identify a preferred system, and acquiringservice associated with the preferred system.

Non-transitory computer readable medium executable by a processor in amobile system for establishing a communication channel between themobile system and a base station in a wireless communication networkincludes at least computer code for computer code for receivinginformation corresponding to a location of a mobile system, computercode for using the location information to identify a preferred system,and computer code for acquiring service associated with the preferredsystem.

A wireless network includes a base station and a mobile system. In thedescribed embodiments, the mobile system determines a current locationof the mobile system by receiving information corresponding to alocation of a mobile system, using the location information to identifya preferred system, and acquiring service associated with the preferredsystem

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof can best beunderstood by reference to the following description taken inconjunction with the accompanying drawings.

FIG. 1 is a diagram of a wireless communication system 100 according toone embodiment that supports a number of users, and which can implementvarious aspects of the invention.

FIG. 2 shows a mobile system using BTS information to determine devicelocation in accordance with the described embodiments.

FIG. 3 shows GEO Locate Table in accordance with the describedembodiments.

FIGS. 4-5 show tagged GEOs in accordance with the described embodiments.

FIG. 6 shows a mobile system using device location information toidentify a first GEO to scan using the GEO Locate Table.

FIG. 7 shows an Extended GEO Locate Table in accordance with thedescribed embodiments.

FIGS. 8-13 show flowcharts detailing processes in accordance with thedescribed embodiments.

FIG. 14 shows a representative mobile system in accordance with thedescribed embodiments.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

In the following detailed description, numerous specific details are setforth to provide a thorough understanding of the concepts underlying thedescribed embodiments. It will be apparent, however, to one skilled inthe art that the described embodiments can be practiced without some orall of these specific details. In other instances, well known processsteps have not been described in detail in order to avoid unnecessarilyobscuring the underlying concepts.

Wireless communication systems are widely deployed to provide varioustypes of communication such as voice, data, and so on. These systems maybe based on code division multiple access (CDMA), time division multipleaccess (TDMA), or some other modulation techniques. A CDMA systemprovides certain advantages over other types of systems, includingincreased system capacity. A CDMA system may be designed to support oneor more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-BaseStation Compatibility Standard for Dual-Mode Wideband Spread SpectrumCellular System” (the IS-95 standard), (2) the standard offered by aconsortium named “3rd Generation Partnership Project” (3GPP) andembodied in a set of documents including Document Nos. 3G TS 25.211, 3GTS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) thestandard offered by a consortium named “3rd Generation PartnershipProject 2” (3GPP2) and embodied in a set of documents including“C.S0002-A Physical Layer Standard for cdma2000 Spread SpectrumSystems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard forcdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High RatePacket Data Air Interface Specification” (the cdma2000 standard), (4)the “TIA/EIA-IS-856 CDMA2000 High Rate Packet Data Air InterfaceSpecification” (the IS-856 standard), and (5) some other standards.

Cellular communication system users commonly have a service agreementwith a cellular provider. The system operated by a cellular provider maycover a limited geographical area. When a user travels outside of thisgeographical area, service may be provided by another system operator,under a roaming agreement. There is often more than one service providerin a particular region, so a user may have a choice as to which serviceprovider to roam with. As cellular communication systems haveproliferated, networks of cellular systems have been organized undercommon service providers, or with contractual agreements between serviceproviders. Roaming fees are minimized or eliminated when a usertransfers between systems which are party to such agreements. As such,modern mobile stations often make use of Preferred Roaming Lists (PRLs),which contain information about the preferred systems for roaming andvarious parameters needed for communication therewith. PRLs may bepre-programmed in a mobile station when service is initiated. The PRL isbasically a binary file loaded in memory of the MS that allows the MS tochoose a best option from all networks available in a visited areaaccording to a strategy specified by specific roaming business rules. Inparticular, the PRL is a database residing in a wireless (primarilyCDMA) device, such as a cell phone, that contains information usedduring the system selection and acquisition process. In the case ofRUIM-based CDMA devices, the PRL resides on the RUIM. The PRL indicateswhich bands, sub bands and service provider identifiers will be scannedand in what priority order. The PRL works sequentially in that the MSscans the PRL for an allowed network from the top of the list andfinishing at the bottom of the list having the potential of a longsearch. Without a PRL, the device may not be able to roam i.e. obtainservice outside of the home area. There may be cases where missing orcorrupt PRL's can lead to a customer not having service at all.

The conventional PRL consists of two tables (along with some header andoverhead information) namely an acquisition table and a system table.The acquisition table can take the form of an indexed list offrequencies on which the MS may search for particular systems. The ideabehind the acquisition table is to optimize the acquisition time byidentifying only the frequencies that should be searched, rather thansearching the entire radio frequency spectrum. Each system table entrybelongs to a geographic area known as a GEO. The GEO is a logical groupof systems (channel, SID, NID) provided by the carrier network andprovisioned in MS. These GEOs are listed in priority order. Each systemcan be identified by either a system identifier/network device (SID/NID)or a GEO. The information contained in each acquisition table entryincludes an index, the network type, and associated channel block. Thesystem table on the other hand can be a prioritized list of systems thatthe device is permitted to access (Preferred Systems) and those that itis explicitly forbidden to access (Negative Systems).

On many networks regularly updating the PRL can be desirable if thesubscriber uses the device outside the home area frequently,particularly if they do so in multiple different areas. This allows thephone to choose the best roaming carriers, particularly “roamingpartners” with whom the home carrier has a cost-saving roamingagreement, rather than using non-affiliated carriers. PRL files can alsobe used to identify home networks along with roaming partners, thusmaking the PRL an actual list that determines the total coverage of thesubscriber, both home and roaming coverage. However, as the number ofentries in the PRL becomes greater, the time required to search anddiscovers a preferred carrier becomes longer. Searching large PRLs canbe prohibitively expensive in both time and power consumption.

Accordingly, the embodiments described herein teach efficient techniquesfor determining a frequency on which a mobile system can camp, thefrequency associated with a preferred carrier or roaming partner. Theefficient techniques can use information received from a base station todetermine a current location of the MS that can be expressed in terms ofa set of approximate coordinates of the mobile system. The set ofapproximate coordinates can take the form of a range of latitude andlongitude. In one embodiment, the information can be received from anycompatible base station noted as being available. The available basestations can include those associated with a preferred or roamingpartner as well as non-preferred. Moreover, information from unavailable(such as emergency) can also be used to determine the current locationof the MS. The current location of the MS can then be used to taginformation in the PRL provisioned in the MS. The tagged information caninclude tagging at least SID data. The tagged SID data can also be usedto identify a corresponding GEO in terms of location data. In this way,once the current location of the MS is determined, the current locationdata can be used to point to the data in the tagged PRL corresponding tothe current location thereby greatly reducing an amount of time andpower consumed in determining an appropriate frequency on which the MScan camp.

In a particular embodiment, the current location of the MS can bedetermined by a location engine, the location engine executed by atleast a processor in the MS. The location engine can determine thecurrent location of the MS by at least receiving a pilot signal from abase station, the pilot signal including at least a sync channel message(SCHM), the SCHM including information indentifying a carrier in theform of of a system identifier/network identifier (SID/NID), or moresimply SID. It is the information included in the SID that the MS usesto query the PRL to determine if the current SID is associated with apreferred carrier and if not is simply identified as being available.Whether or not the SID is associated with the preferred carrier orroaming partner, the information provided by the SCHM can be used todetermine the approximate location of the base station. By approximatelocation, it is meant that a range of longitude and latitudes associatedwith the base station can be provided.

In order to determine the approximate location of the base station, thelocation engine can use a time differential between a local clockassociated with the base station and a standard clock can be decodedfrom the SCHM. As is well known in the art, the time differential can beused to estimate a current longitude of the base station (due to theknown rotational speed of the Earth and a known reference longitude,which is typically taken as 0° longitude). In a particular embodiment,the time differential can be the time differential between the localtime of the base station and co-ordinate Universal Time, or UTC, alsoreferred to as a local time offset, or more simply LTM_OFF. Determiningthe current longitude from the LTM_OFF can provide an estimate of thelongitude of the base station (and also that of the MS) to approximately±15 minutes. Additional geographical information can be provided fromthe base station in the form of Global Positioning System (GPS) baseddata that can provide an estimate of the current location in terms of arange of latitudes (as well as longitudes). The additional geographicaldata can be used to provide an estimate of a current location of thebase station (and the MS) that in turn can be used to tag the SIDincluded in the pilot signal.

Once the location engine has determined the current location of the MS,the PRL can be tagged such that device location data can be associatedwith a particular SID. The PRL can be tagged by, for example, adding alocation table to the PRL, the location table can include devicelocation information. The device location information can point to atleast one SID entry in the PRL. Moreover, the tagged SIDs can, in turn,be used to define a corresponding GEO in terms of location dataproviding an efficient mechanism for providing a first GEO for scanning.In this way, the MS can use the information provided in a first scan todetermine an estimate of a current geographical location of the basestation (and the MS) in terms of a range of latitudes and longitudes.The estimated location information can then be used to specify thoseSIDs in the PRL that are associated with the current geographicallocation. In this way, the MS need only scan those frequenciescorresponding to the current geographical location and no others inorder to find an appropriate frequency on which to camp. The reducedsearching can greatly reduce an amount of time and battery powerrequired for the MS to establish a connection with a preferred carrieror roaming partner.

Moreover, GEOs provisioned in the PRL provided by a service carrier canbe defined in terms of location data. The location data can then be usedto quickly identify a current GEO based upon device location informationgenerated by the location engine. Once identified as the current GEO, aprecise scan list can be provided from those SIDs associated with thecurrent GEO. The data in the scan list can be conditioned in order toreduce a number of potential scan operations. For example, in oneembodiment, the scan list can be conditioned based upon a list of mostrecently used SIDs. In this way, the number of scans can be limited tothose SIDs most likely to be appropriate. This is typically the casewhen a loss of signal within a local geographical area requires a newconnection with the service provider be established. Since the loss ofsignal was likely due to local conditions, it is likely that the mostrecently used SID will have a high probability of being at least one ofthe preferred SIDs. One of the advantages of providing the currentlocation data as a range of latitudes and longitudes is related to thepossibility that a SID can straddle or be included in more than one GEO.In this way, by expressing the location data in terms of the range oflatitude and longitude provides for the possibility of scanning morethan one GEO thereby greatly increasing the likelihood of discover anappropriate frequency on which the MS can camp.

It should be noted that the updating of the enhanced PRL can be ongoingand dynamic in nature particularly in those cases where the user of theMS travels between a numbers of different GEOs. In this situation, theentries in the location data table corresponding to the SIDs in the GEOsmay be blank (if the location has not been previously visited) orinvalid having location data inconsistent with current location data.Therefore, as the user of the MS travels about, the location dataincorporated into the enhanced PRL can also increase providing a dynamicand robust database.

In some cases, an entirely new SID can be encountered (or a carrier canmodify and change a SID to be included in a different GEO, for example)which was not part of the original PRL. In this case, the enhanced PRLcan include the new SID as part of a list of new entries data base thatcan be appended to the enhanced PRL. However, in this case, the list ofnew entries data base can be added to include a channel numberassociated with the new SID entry.

The PRL can include at least a SID entry, an associated GEO indicator,and location information in the form of a range of latitude andlongitudes for each SID/NID pair, GEO included in the PRL. For example,in addition to the system table and the acquisition table, the PRL caninclude a location table. The location table can include locationinformation in the form of a range of latitude and longitude associatedwith a particular SID/NID pair. This location information can be used toquickly identify a SID/NID on which the MS can camp. If a discoveredsystem in not reflected in the PRL as a preferred system or a roamingpartner, then that system can be designated as an available system.Information associated with the available system can be buffered andused as a fall back system (i.e., if it is determined that no preferredsystems of roaming partners are available). However, information fromthe available system can be used to determine location data of the basestation. The location data can then be used to update the enhanced PRL,if necessary.

These and other embodiments are discussed below with reference to FIGS.1-11. However, those skilled in the art will readily appreciate that thedetailed description given herein with respect to these figures is forexplanatory purposes only and should not be construed as limiting.

FIG. 1 is a diagram of a wireless communication system 100 according toone embodiment that supports a number of users, and which can implementvarious aspects of the invention. System 100 may be designed to supportone or more CDMA standards and/or designs (e.g., the W-CDMA standard,the IS-95 standard, the cdma2000 standard, the IS-856 standard). Forsimplicity, system 100 is shown to include three base stations (BTS) 104in communication with two mobile stations (MS) 106 each of which canencompass fixed wireless applications. In the context of thisdiscussion, the term mobile station (MS) can be used interchangeablywith the terms user equipment (UE), subscriber unit (SU), subscriberstation (SS), access terminal (AT), remote terminal (RT), or othercorresponding terms known in the art. It should be noted that a basestation and the associated coverage area are often collectively referredto as a “cell”. For example, in IS-95 systems, a cell may include one ormore sectors. However, in the W-CDMA specification, each sector of abase station and the sector's coverage area can be referred to as acell. Depending on the CDMA system being implemented, MS 106 cancommunicate with one (or possibly more) base stations on a forward linkat any given moment and with one or more base stations on a reverse linkdepending on whether or not the mobile station is in soft handoff. Inthe context of this discussion, the forward link (i.e., downlink) refersto transmission from the base station to the mobile station, and thereverse link (i.e., uplink) refers to transmission from the mobilestation to the base station.

BTS 104 can dedicate a significant amount of output power to a pilotchannel that can include sub-channels in the form of a sync channel thatcontinually transmits a sync channel message (SCHM). The SCHM cancontain information about the network including system identifiers(SID), network identifiers (NID) and a local time offset (LTM_OFF). Aswell known in the art, the local time offset indicates a differencebetween current time and correlated universal time, or UTC. In this way,an approximate value of a current longitude of BTS 104 (and byassociation MS 106) can be determined. It should be noted that timezones can be written as offset from UTC in the format ±[hh]:[mm],±[hh][mm], or ±[hh]. So if the time being described is one hour ahead ofUTC (such as the time in Berlin during the winter), the zone designatorwould be “+01:00”, “+0100”, or simply “+01”. It should be noted that theoffset from UTC changes with day light saving time. For example, a timeoffset in Chicago would be “−6:00” for the winter (Central StandardTime) and “−5:00” for the summer (Central Daylight Time). BTS 104 canalso transmit base station latitude information that can take the formof a data field referred to as BASE_LAT that can convey the latitude ofthe BTS 104 in units of 0.25 s (econds).

As shown in FIG. 2, when “searching”, MS 106 can find pilot signals fora wireless network by tuning to particular radio frequencies. MS 106 canreceive pilot signal 202. MS 106 can listen to the sync channelassociated with pilot signal 202 and decode the corresponding SyncChannel Message (SCHM) 204. SCHM 204 can include information such as(system identifier) SID 206, (local time offset) LTM_OFF 208, and(daylight savings time offset) DAYLT 210. Location engine 212 in MS 106can use the information from the decoded SCHM (in particular values ofSID 206) to compare to values of SID provisioned in PRL 214 stored in MS106. It should be noted that the information included in SCHM 204 can beconsidered reliable information. In accordance with ANSI-41 StandardsTechnology (IFAST), any SID can be mapped to a country (MCC). In thisway, a list of SIDs (referred to as SID table 216) can be sorted by SIDranges and stored in MS 106. Upon decoding SCHM 204, MS 106 can executea table lookup to determine the country in which MS 106 is currentlylocated. In the described embodiment, SID table 216 can be stored as anarray of SIDs and corresponding Mobile Country Codes (MCC).

In some cases, a particular SID can be mapped to multiple country codes.In this case, the country code associated with the current location ofMS 106 can be determined using LTM_OFF 208 and DAYLT 210. In oneembodiment, LTM_OFF 208 and DAYLT 210 can be stored in MS 106 as LTMtable 218. In this way, LTM_OFF 208 and DAYLT 210 received from SCHM 204can be used to index LTM table 218 to determine the proper country codeMCC in which MS 106 is currently located. In this way, LTM_OFF 208 andDAYLT 210 can be used to determine estimated current location(EST_LOC_(current)) 220 of BTS 104 (and MS 106). EST_LOC_(current) 220can then be used to update location table 222. By updating it is meantthat the entry corresponding to SID_(current) in SID table 216 can belinked with (also referred to as tagged) with location informationcorresponding to EST_LOC_(current) 220. In this way, using locationtable 222 each SID entry in PRL 214 can be annotated with correspondinglocation data. In the described embodiment, the location data can takethe form of a range of latitudes and longitudes thereby enlarging ageographical region associated with a particular SID and increasing thelikelihood of a particular location matching a corresponding SID.

In some cases, MS 106 can use a paging channel (PAGECH) in which BST 104periodically transmits a system parameter message, or SPM. The SPM caninclude information such as base station latitude (BASE_LAT) and basestation longitude (BASE_LONG) each being associated with GlobalPositioning System (GPS) co-ordinates of the base station. In this way,a more precise indication in the form of an enhanced location ENH_LOC ofMS 106 can be provided. In the described embodiment, the estimatedlocation EST_LOC 220 can be used to validate the BASE_LAT and BASE_LONGinformation and if validated can be used to triangulate the devicelocation (dev_loc) of MS 106 within a country (MCC) and within a rangeof latitude and longitude.

In order to most efficiently acquire a preferred system, a current GEOmust first be identified. As well known in the art, a GEO is a logicalgroup of systems (channel, SID, NID) provided by the carrier network andprovisioned in MS 106 as the system table of PRL 214. It should be notedthat each GEO can be provisioned in the system table of PRL 214 by thecarrier. The system GEO can map to a physical geographical region withinthe carrier network's scope of operation. However, since the system GEOcan be defined in terms of individual SIDs, by tagging each SID withcorresponding device location information, the system GEO can also bedefined in terms of device location information using the tagged SIDs asshown in FIG. 3 illustrating GEO Locate Table 300. In this way, thelocation GEO tagged with corresponding device location data can be usedto provide a more precise scan list for MS 106 by using the devicelocation information provided by location engine 212.

In order to provide a more effective and efficient scan search, the GEOprovisioned in the system table of PRL 214 (referred to hereinafter asGEO_(system)) can be re-defined as a device location dependent GEO(GEO_(locate)) by tagging each GEO with appropriate device locationdata. GEO locate table 300 can be used to define a GEO using devicelocation data, which may or may not coincide with the GEO originallyprovisioned in MS 106. For example, as shown in FIG. 3 GEO Locate Table300 can include entries in which a GEO can be defined in terms of devicelocation values (dev_loc). By tagging each GEO with corresponding devicelocation values (EST_LOC) provided by location engine 212 can be used toquickly identify the current GEO. Once the current GEO has beenidentified, a more precise scan list can be provided from the SIDsassociated with the identified current GEO.

For example, FIG. 4 shows representative system GEOs, GEO1 _(system) andadjacent GEO2 _(system) where each GEO can be defined in terms ofindividual SIDs. For this example, GEO1 _(system) is defined as SID1through and including SID6 where SID4 and SID3 overlap GEO1 _(system)and GEO2 _(system). In this situation, if MS 106 was located in aboundary area between GEO1 _(system) and GEO2 _(system) (SID3 or SID4,for example) when losing a signal, in order to re-establish theconnection, a conventionally provisioned PRL could possibly lead to MS106 to change from GEO1 _(system) to GEO2 _(system) to start searchingwhich can be very time consuming. However, since GEO1 _(system) can bedefined in terms of SID1 . . . SID6, each of which can in turn be taggedwith device location, GEO1 _(system) can also be tagged with devicelocation data along the lines shown in FIG. 5. In this way, any devicelocated within the range of latitude and longitude associated with GEO1_(location) will use GEO1 _(location) as a first GEO in a search therebysubstantially reducing an amount of time or power required to find afrequency on which MS 106 can camp. For example, as shown in FIG. 6, ifMS 106 is located at point A near the boundary of GEO1 _(system) andGEO2 _(system), MS 106 can query GEO locate table 300 to determine thatGEO1 _(locate) is the first GEO to scan thereby avoiding the possibilityof using GEO2 _(system) as the first GEO to scan.

In this way, since each SID tagged with specific location data that cantake the form of a range of latitude and longitude, the tagged SIDstaken together can re-define the GEO from that originally provisioned inPRL 214 using the device location information. This can be particularlyadvantageous in situations where MS 106 is near a boundary between twodifferent GEOs and must re-establish the connection with the serviceprovider. This can happen when, for example, MS 106 experiences a lossin signal in a tunnel and such. For example, if MS 106 is currentlycamped on SID3 in GEO1 and SID3 is included in GEO1 and GEO1,re-establishing a connection between the service provider and MS 106 canrequire that MS 106 change from GEO1 to GEO2 which can take a lot oftime. However, using the data stored in GEO locate table 300, thecurrent location of MS 106 can indicate that GEO1 be designated as thefirst GEO to scan.

As shown in FIG. 7, GEO locate Table 300 can be extended to includelocation data for each SID and additional fields for available systemsthat are not provisioned in PRL 214. Location engine 212 can update GEOLocate Table 300 whenever MS 106 acquires service on a systemprovisioned in PRL 214. The SID of the acquired system can be taggedwith the location data (dev_loc) provided by location engine 212.Tagging the SIDs can alter the GEO boundaries of MS 106 (as shown inFIG. 6). In this way, the GEO organization represented by GEO LocateTable 300 can be more specific and customized to a user than thatprovisioned in MS 106 by the service provider.

In some situations, a system not provisioned in PRL 214 on which MS 106is able to successfully camp and originate a call can also be enteredinto GEO Locate Table 300 since call origination can validate theavailable system as a potential PRL system. Adding the available systemto GEO Locate Table 300 to form Extended GEO Locate Table 700 can havethe effect of extending a limited or an out of data provisioned PRL. Inthis way, MS 106 can possibly violate some rules of limited roaming,therefore, MS 106 can only use the non-PRL systems in the scan list onlyif MS 106 is configured for roaming. Furthermore, any system notprovisioned in PRL 214 added to Extended GEO Locate Table 700 can alsocontain an associated channel number that can be used while building anoptimized scan list.

During a system scan operation, location engine 212 can use devicelocation information dev_loc to index into GEO Locate Table 300 orExtended GEO Locate Table 700 to generate an optimized scan list havingmatching dev_loc information. The optimized scan list can include atleast channel numbers form the PRL associated with the SIDs matching thedevice location information dev_loc and channel numbers form GEO LocateTable 300 or 700 that are associated with the SIDs matching the devicelocation information dev_loc. It should be noted that if MS 106 isrequired to enforce limited roaming, the MS 106 can turn off thisparticular feature.

FIG. 8 shows a flowchart describing process 800 in accordance with thedescribed embodiments. Process 800 can be used to provide an efficienttechnique for camping on a wireless network operated by a preferredcarrier (or a roaming partner). Process 800 can use system informationfrom an available but not preferred system (or not a roaming partner) todetermine a reasonably good estimate of a current location of a mobilestation, or MS. The mobile station can include system information stored(provisioned) in a data base referred to as a preferred roaming list, orPRL. The PRL can be structured to include specific frequency informationassociated with particular mobile operators. Process 800 can use thecurrent location of the mobile system to avoid scanning frequencies notassociated with a preferred provider or roaming partner.

Accordingly, process 800 can begin at 802 by powering on a mobile system(MS). By powering on it is meant that MS must reacquire access to awireless network operated by a preferred carrier or a designated roamingpartner. Typically, the re-acquisition of access can begin at 804 by theMS scanning a most recently used frequency. Using the most recently usedfrequency to initiate the search for a current frequency can be basedupon the idea that typically the MS was merely turned off or wastemporarily disconnected from the wireless network but still remainswithin the immediate geographical area. Scanning by the MS can includesearching for a pilot signal, the pilot signal being broadcast by a basestation. In this way, the MS can potentially detect a pilot signal frommany base stations of which only a handful can be associated with thepreferred wireless network carrier. Once the MS has detected the pilotsignal, the MS can receive information from the base station at 804. TheMS can decode the pilot signal to obtain information from a sync channelmessage (SCHM) at 806 that can include such information as a systemidentifier (SID) and associated network identifier (NID), a local timeoffset from coordinated UTC (LTM_OFF), and a daylight savings timecorrection factor (DAYLT).

At 808, a preferred roaming list (PRL) provisioned in the MS can bequeried by comparing the SID/NID form the SCHM to those values stored inthe PRL. It should be noted that the PRL can take the form of a list ofSID/NID, associated frequencies, and corresponding geographicallocations, referred to as GEOs, corresponding to particular SIDs. GEOcan typically take the form of Mobile Country Codes, or MCCs. At 810, adetermination is made whether or not the SID/NID is stored in the PRL aseither a preferred carrier or as a roaming parameter. If the SID/NID isdetermined to be stored in the PRL as a preferred carrier, then at 812,the MS camps on the frequency associated with the base station and storethe information at 814. On the other hand, if the SID/NID is notdetermined to be associated with the preferred carrier or roamingpartner, then at 816, the carrier is designated as available (notpreferred or roaming) and information provided by the available carrieris stored in the MS. At 818, the stored information is used to determinea current location of the MS. The current location information is thenused to SIDs from the PRL at 820. At 822, the MS directly jumps to theidentified frequency(ies) skipping over any intervening frequencies. Inthis way, the amount of time and power consumed in camping on apreferred (or roaming partner) provider can be substantially reduced.

Once the estimate of the current location is known, MS 106 can use thecurrent location information to more effectively query PRL stored in MS106 jumping directly to only those frequencies associated with thecurrent location. In this way, only those frequencies associated withthe current location can be scanned avoiding scanning those frequenciesnot associated with the current location.

FIG. 9 shows a flowchart detailing process 900 as a particularembodiment of step 818 of process 800. Accordingly, process 900 can beperformed by the MS. The MS can use information received from the basestation and stored in the MS to determine a current location of the MS.The information received from the base station and stored in the MS caninclude at least a SID/NID corresponding to the base station. Therefore,at 902, an SID table stored in the MS can be queried using the SID/NIDinformation received from the base station. In the described embodiment,the SID table can include an array of SID values and correspondingMobile Country Codes, or MCCs. At 904, an MCC corresponding to thereceived SID is identified. At 906, if the received SID is determined tobe mapped to more the one MCC, then at 908, a local time offset value(LTM_OFF) and daylight correction value (DAYLT) obtained from the basestation are each used to identify the MCC corresponding to the basestation and at 910, the LTM_OFF and DAYLT are used to identify thelongitude of the country associated with the identified MCC as est_loc.Returning to 906, if is determined that the SID is not mapped to morethan one MCC, then at 912, the proper MCC is identified and at 910, theest_loc is determined as above.

FIG. 10 shows a flowchart detailing process 1000 arranged to provide anenhanced location determination when a paging channel is available.Accordingly, at 1002 if the paging channel is not available, the process1000 ends, otherwise, at 1004 a system parameters message (SPM) isreceived as part of the paging channel (PAGECH). The SPM can include GPSco-ordinate data that can include base station longitudinal (BASE_LONG)data and base station latitude (BASE_LAT) data. Therefore, at 1006, GPSco-ordinates data is decoded from the SPM and at 1008, the GPS data isused to determine enhanced coordinate of the MS (referred to as en_loc).By enhanced it is meant that the accuracy of the estimated location canbe better than that of est_loc. In order to determine if en_loc isvalid, enh_loc is compared to est_loc at 1010 and if the comparison isdetermined to be valid at 1012, then at 1014 the enh_loc and est_loc areused to triangulate a current range of latitudes/longitudescorresponding to the current location.

FIG. 11 shows a flowchart detailing process 1100 in accordance with thedescribed embodiments. Process 1100 can be used for updating a GEOLocate Table with device location information, the device locationinformation being used to tag a SID provisioned in a PRL stored in amobile system. Process 1100 can be carried out by the mobile system (MS)acquiring service on a system provisioned on the PRL. By provisioned onthe PRL it is meant that the system identifier (SID) of the acquiredsystem is listed on the PRL. Since the MS was able to acquire theservice, the service can be considered available. However, even thoughthe service can be considered available, the service may not beprovisioned on the PRL if the service is not a preferred service nor isnot a roaming partner. In any case, when the SID of the acquired serviceis included in the provisioned PRL, then at 1104, the SID associatedwith the acquired service is tagged with the location informationassociated with the MS. The location information generated by thelocation engine based at least in part on information provided by thebase station in communication with the mobile system and associated withthe acquired service. Next, at 1106, the GEO Locate Table is updatedwith the tagged SID.

FIG. 12 shows a flowchart detailing process 1200 in accordance with thedescribed embodiments. Process 1200 can be used to update a GEO LocateTable with device location information, the device location informationbeing associated with a system having an SID not provisioned in the PRL.Accordingly, process 1200 can be carried out by the MS acquiring serviceon a system not provisioned in the PRL at 1202. At 1204, the SID of thesystem not provisioned in the PRL is tagged with device locationinformation received from the location engine, the device locationinformation associated with the mobile system. Next, at 1206, the taggednon-PRL SID is added to the GEO Locate Table and at 1208, the channelnumber of the non-PRL SID is added to the GEO Locate Table.

FIG. 13 shows a flowchart detailing process 1300 in accordance with thedescribed embodiments. Process 1300 can be used to generate a scan listoptimized for a geographical location of a mobile system. Process 1300can begin at 1302 by receiving device location information, the devicelocation information can be provided by the location engine included inthe mobile system. Next at 1304, the GEO Locate Table is indexed usingthe device location information. At 1306, a first set of channel numbersare received from the GEO Locate Table. The first set of channel numbersassociated with the SIDs in the GEO Locate Table matching the devicelocation information. At 1308, a second set of channel numbers arereceived from the GEO Locate Table. The second set of channel numbersassociated with SIDs from the PRL provisioned in the MS matching thedevice location information. At 1310, the optimized scan list isgenerated using the first and second set of channel numbers.

FIG. 14 shows an embodiment of mobile unit 1400. For clarity, only asubset of the components is shown. Signals are received at antenna 1410,and delivered to receiver 1420 where amplification, down-conversion,sampling, and demodulating takes place. Various techniques for receivingCDMA signals are known in the art. In addition, the principles of thepresent invention apply with equal force to wireless communicationsystems deploying air interfaces other than those based on CDMA.Receiver 1420 is in communication with a central processing unit (CPU)1430. CPU 1430 may be a microprocessor or digital signal processor(DSP), or one of various processors known in the art. CPU 1430communicates with memory 1440, which is shown containing roaming list1460. The roaming list 1460 can be programmed via over-the-airprogramming in conjunction with antenna 1410 and receiver 1420, or thedata for the roaming list may come in from other inputs to CPU 1430 (notshown). CPU 1430 is also connected to transmitter 1450, for transmittingmessages, data, voice, etc., using any of the techniques fortransmission known in the art. Transmitter 1450 is connected to antenna1410, for transmission to a base station, such as base station 104.Receiver 1420 and transmitter 1450, in conjunction with antenna 1410,can be used to communicate with one or more systems identified in theroaming list 1460 when the mobile station is roaming.

The various aspects, embodiments, implementations or features of thedescribed embodiments can be used separately or in any combination.Various aspects of the described embodiments can be implemented bysoftware, hardware or a combination of hardware and software. Thedescribed embodiments can also be embodied as computer readable code ona non-transitory computer readable medium. The computer readable mediumis defined as any data storage device that can store data which canthereafter be read by a computer system. Examples of the computerreadable medium include read-only memory, random-access memory, CD-ROMs,DVDs, magnetic tape, and optical data storage devices. The computerreadable medium can also be distributed over network-coupled computersystems so that the computer readable code is stored and executed in adistributed fashion.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not intended to be exhaustive or to limit theembodiments to the precise forms disclosed. It will be apparent to oneof ordinary skill in the art that many modifications and variations arepossible in view of the above teachings.

The embodiments were chosen and described in order to best explain theunderlying principles and concepts and practical applications, tothereby enable others skilled in the art to best utilize the variousembodiments with various modifications as are suited to the particularuse contemplated. It is intended that the scope of the embodiments bedefined by the following claims and their equivalents.

What is claimed is:
 1. A method, comprising: receiving, at a mobile system, a message from a base station, the message including a system identifier (SID) and time information that identifies the base station; estimating a first location of the mobile system based on the time information, the estimated location identifying a location within a country; using the estimated first location to identify a preferred system; acquiring service associated with the preferred systems; associating the acquired service with a geographical region in a locate table, wherein the geographical region is further associated with a range of geographic coordinates; subsequent to the estimating of the first location, estimating a second location of the mobile system, wherein the second location is outside of the range of geographic coordinates; and updating the range associated with the geographical region to include the second location.
 2. The method as recited in claim 1, wherein the geographical region locate table is used to identify the preferred system.
 3. The method as recited in claim 1, wherein the geographical region is further associated with a Preferred Roaming List (PRL) indicator indicating that the SID is provisioned in a PRL stored in the mobile system.
 4. The method as recited in claim 1, further comprising: identifying a second SID associated with the acquired service, wherein the geographical region is associated with the second SID, wherein updating the range associated with the geographical region includes updating a range of geographic coordinates associated with the second SID.
 5. The method as recited in claim 1, further comprising: determining that the SID is not associated with the preferred system, wherein the determination is made by using the geographical region locate table.
 6. The method as recited in claim 1, further comprising: building a scan list based on channels associated with the geographical region in the geographical region locate table, and using the scan list to acquire the preferred system.
 7. The method as recited claim 6, further comprising; scanning the optimized scan list to acquire access to the preferred system.
 8. The method as recited in claim 1, wherein the estimated location includes a geographic coordinate.
 9. The method as recited in claim 1, wherein the estimated location includes a range of locations.
 10. The method as recited in claim 1, wherein the time information includes a time offset.
 11. A wireless mobile system, comprising: a wireless interface, the wireless interface configured for wirelessly communication with a wireless base station; a memory device, the memory device arranged to store data, the data including at least a preferred roaming list (PRL); and a processor, the processor coupled to the wireless interface and the memory device, the processor arranged to: access, at a mobile system, a message received from a base station, the message including a system identifier (SID) and time information that identifies the base station; estimate a first location of the mobile system based on the time information, the estimated location identifying a location within a country; use the estimated first location to identify a preferred system; acquire service associated with the preferred system; associate the acquired service with a geographical region in a locate table, wherein the geographical region is further associated with a range of geographic coordinates; subsequent to the estimating of the first location, estimate a second location of the mobile system, wherein the second location is outside of the range of geographic coordinates; and update the range associated with the geographical region to include the second location.
 12. The wireless mobile system, as recited in claim 11, wherein the geographical region locate table is used to identify the preferred system.
 13. The wireless mobile system, as recited in claim 11, wherein the geographical region is further associated with a Preferred Roaming List (PRL) indicator indicating that the SID is provisioned in a PRL stored in the mobile system.
 14. The wireless mobile system, as recited in claim 11, wherein the processor is further arranged to: identify a second SID associated with the acquired service, wherein the geographical region is associated with the second SID, wherein updating the range associated with the geographical region includes updating a range of geographic coordinates associated with the second SID.
 15. The wireless mobile system, as recited in claim 11, wherein the processor builds a scan list based on channels associated with the geographical region in the geographical region locate table and scans the scan list to acquire access to the preferred system.
 16. Non-transitory computer readable medium for storing program code executable by a processor in a wireless mobile system in a wireless communication network, comprising: computer code for receiving, at a mobile system, a message from a base station, the message including a system identifier (SID) and time information that identifies the base station; computer code for estimating a first location of the mobile system based on the time information, the estimated location identifying a location within a country; computer code for using the estimated first location to identify a preferred system; computer code for acquiring service associated with the preferred system; computer code for associating the acquired service with a geographical region in a locate table, wherein the geographical region is further associated with a range of geographic coordinates; computer code for, subsequent to the estimating of the first location, estimating a second location of the mobile system, wherein the second location is outside of the range of geographic coordinates; and computer code for updating the range associated with the geographical region to include the second location.
 17. The computer readable medium as recited in claim 16, wherein the geographical region locate table is used to identify the preferred system.
 18. The computer readable medium as recited in claim 16, wherein the geographical region is further associated with a Preferred Roaming List (PRL) indicator indicating that the SID is provisioned in a PRL stored in the mobile system.
 19. The computer readable medium as recited in claim 16, further comprising: computer code for identifying a second SID associated with the acquired service, wherein the geographical region is associated with the second SID, wherein updating the range associated with the geographical region includes updating a range of geographic coordinates associated with the second SID.
 20. The computer readable medium as recited in claim 16, further comprising: computer code for building a scan list based on channels associated with the geographical region in the geographical region locate table, and computer code for using the scan list to acquire the preferred system.
 21. The computer readable medium as recited claim 16, further comprising; computer code for determining that the SID is not associated with the preferred system, wherein the determination is made by using the geographical region locate table.
 22. A wireless network, comprising: a base station; and a mobile system, wherein the mobile system is configured to: access, at a mobile system, a message received from a base station, the message including a system identifier (SID) and time information that identifies the base station; estimate a first location of the mobile system based on the time information, the estimated first location identifying a location within a country; use the estimated first location to identify a preferred system; acquire service associated with the preferred system; associate the acquired service with a geographical region in a locate table, wherein the geographical region is further associated with a range of geographic coordinates; subsequent to the estimating of the first location, estimate a second location of the mobile system, wherein the second location is outside of the range of geographic coordinates; and update the range associated with the geographical region to include the second location.
 23. The wireless network as recited in claim 22, wherein the geographical region locate table is used to identify the preferred system.
 24. The wireless network as recited in claim 23, wherein the geographical region is further associated with a Preferred Roaming List (PRL) indicator indicating that the SID is provisioned in a PRL stored in the mobile system.
 25. The wireless network as recited in claim 23, wherein the mobile system is further configured to identify a second SID associated with the acquired service, wherein the geographical region is associated with the second SID, wherein updating the range associated with the geographical region includes updating a range of geographic coordinates associated with the second SID.
 26. The wireless network as recited in claim 23, wherein the mobile device builds a scan list based on channels associated with the geographical region in the geographical region locate table, uses the scan list to acquire the preferred system and scans the optimized scan list to acquire access to the preferred system. 